ANATOMICAL STRUCTURE OF ANTHROPOID APES. 155 



Aubry chimpanzee (Plate ix. Fig. 1, 15) with the 

 risorius strongly developed. I have not observed 

 this formation either in the orang or the gibbon, 

 but it was apparent in one of the ateks (Atelcs 

 leucophthalmos). In this case the muscle covered 

 the platysma myoides and Stenson's duct, i.e. the 

 duct leading out of the parotid gland (Fig. 50, *). 



For some time I was disposed to regard the risorius 

 of this ape as only a radiation of the platysma 

 myoides, but my ojiinion upon this point is again 

 shaken. 



In the gorilla a faint depressor anguli oris and an 

 equally faint depressor labii inferioris may be ob- 

 served, the latter partly covered by the Inrge and 

 predominant orbicularis oris (Fig. 50). In the chim • 

 panzee the two depressors are plainly apparent, and 

 in the gibbon the one first named was at any rate 

 developed. The platysma myoides, the depressors 

 just mentioned, and the crescent-shaped orbiculares 

 are in this animal in close connection with each other. 

 Froriep's suggestion becomes ever more probable, 

 that these muscles of the lower lip owe their origin 

 to the intersection of the opposite portions of the 

 skin-muscles of the neck which overlap the face. The 

 buccinator muscle in anthropoids resembles on the 

 whole that of man, and in both cases is pierced by 

 Stenson's duct (Fig. 50). The form of the mas- 

 seter muscle is common to both (see Fig. 50, 11, le). 

 In the external ear of anthropoids there is an attra- 

 hens, attollens, retrahens (Fig. 50). Compared with 

 that of a white man, and still more with that of 

 a negro (see Figs. 48, 19, and 49, 17), the attollens is 



